When it is necessary to perform deep hole drilling into a slanting surface, conventionally a seating face is machined in advance using a 2-Flute square end mill, and then the hole is machined using a drill. The center of the tip side of a square end mill has a depressed shape, so the center of the bottom face that has been machined in advance with the square end mill is a protruding machined surface, and thus there is a possibility that when subsequently machining the hole using a drill the machining will be carried out with the drill in a slanted state. Also, when machining a spot faced hole, it is required that the machined bottom face is flat.
Therefore, in Patent Document 1, a drill for spot facing to provide a flat machined bottom face is disclosed with a tip angle of 170 to 190°, a drill web thickness of 0.20 to 0.40 times the drill diameter, the concavity depth of the cutting edges is from 0.01 to 0.06 times the drill diameter, and the receding angle of the outer peripheral ends of the cutting edges is from −1 to −20°. In the drill according to Patent Document 1, the opening angle of a flute provided in the rotational direction on the cutting edges is greater than 90°. Also, in Patent Document 2, a drill is disclosed in which the opening angle (flute width) of the flute provided on the cutting edges in the rotational direction is from 75 to 85°, the concavity depth on the cutting edge side is from 0.03 to 0.07 times the drill diameter, and the concavity depth on the heel side is from 0.35 to 0.70 times the drill diameter. Also, by making the opening angle of the flute from 75 to 85°, the chips are curled small, and the chip evacuation performance is increased.